1. Field of the Invention
The present invention relates to fluid film bearings. In more particular aspects, the invention relates to improved motor bearings for electrical submersible pumps and the like whose motor shafts are maintained in a substantially vertical position during operation.
2. Description of the Related Art
Electrical submersible pumps (ESP""s) include an electric motor and a pump that is used to pump oil or other fluids within a wellbore. The electric motors have a rotatable rotor that is contained within a stationary stator. The rotors for the submersible pumps are usually disposed in a substantially vertical position by virtue of their placement in wellbores, which typically are vertical shafts. Therefore, during operation, the rotor shaft of the motor is oriented in the vertical position.
The bearings which surround the rotor shaft are often of the fluid film variety. However, fluid film bearings require a side load to provide optimal dynamic stability. Since the rotor shaft is rotating in a vertical position, there is little or no side load being applied to the bearing during operation. This causes instability in the bearings, which results in excessive motor vibration. Excessive vibration in the bearings can cause the bearing sleeves to break through the oil film resulting in metal to metal contact that can lead to premature wear and motor failure.
Alternative bearing systems have not proven effective in the long term. High wellbore temperatures make elastomers undesirable in such a bearing, particularly as a wear surface. Friction fit rotor bearing assemblies tend to become loose as temperatures change in the wellbore.
Fluid film bearings or bearings that support the shaft of a rotor on fluid are not new. For example, U.S. Pat. No. 3,118,384 issued to Sence et al. describes fluid pressure bearings wherein high pressure fluid is injected to prevent the rotor from contacting the stator. U.S. Pat. No. 3,196,301 issued to Turk discusses fluid film bearings and describes a technique for using an impeller to axially draw fluid in to the bearing to provide clearance between the rotor and stator. However, these arrangements are, in practice, vulnerable to damage from vibration of the rotor shaft within the stator. Mere flowing of fluid around the rotor does not provide effective resistance or dampening of strong vibrations, such as tend to occur in downhole motors.
It would be desirable to have devices and methods that address the problems of the prior art.
A novel bearing assembly and bearing system for a motor is described wherein a fluid shock absorber is provided to cushion and dampen vibration of the rotor shaft. Lubricating fluid is supplied under pressure to lubricate and replenish the fluid film located between the rotating, inner bearing sleeve and the outer, stationary sleeve insert of the bearing assemblies of a motor. The sleeve insert is provided with fluid metering passages that permit lubricating fluid to pass through the body of the sleeve insert. The sleeve insert is disposed radially within a sleeve insert holder, and a fluid gap is defined between the two components.
During operation, vibration of the rotor shaft within the stator bore is damped by the fluid spring created by the metering of fluid through the sleeve insert. As a result, friction is reduced and the lifespan of the motor increased.